1. Biomechanics of Human Movement
Biomechanics of Balance

2. Biomechanics of Balance Topics
Applications Relating to Biomechanics of Balance
Determinants of Stability
Factors Influencing Stability
Role of Sensory Input in Balance
CNS Strategies for the Maintenance of Balance
Enhancing Balance
Assessment of Balance

3. Biomechanics of Balance Applications
Incidence of Falls

4. Biomechanics of Balance Incidence of Falls
1.8 million falls among elderly result in medical treatment
1/3 of all Community-dwelling adults experience at least one fall yearly
Sixth leading cause of death in over 65 age group

5. Biomechanics of Balance Applications
Incidence of Falls
Economic Impact of Falls

6. Falls…..Economic Impact
16.4 Billion Dollars annually
Average cost per fall - $9400
48% of cost paid by Medicare

7. Biomechanics of Balance Applications
Incidence of Falls
Economic Impact of Falls
Influence of Pathology and Injury on Balance

8. Falls…..Influence of Pathology on Balance
Head Injury
Stroke
Vestibular Dysfunction
Orthopaedic Joint Injury
Parkinson’s Disease
Alzheimer’s Disease
Degenerative Joint Disease
Muscle Atrophy
Diminished Balance

9. Biomechanics of Balance Applications
Incidence of Falls
Economic Impact of Falls
Influence of Pathology and Injury on Balance
Relationship between balance and posture – implications

10. Balance – Influence on Posture

11. Biomechanics of Balance Applications
Incidence of Falls
Economic Impact of Falls
Influence of Pathology and Injury on Balance
Relationship between balance and posture – implications
Sport Considerations
Performance
Injury Prevention

12. Biomechanics of Balance Sport Considerations
Performance
Injury Prevention

13. Biomechanics of Balance What Causes Instability?
Destabilizing “External “Torques Act on Segments 
Gravity
Distribution and Position of Mass
Inertia
External Forces

14. Biomechanics of Balance What Produces Stability?
Stabilizing “Internal Torques” Act on Segments
Muscle Forces
Ligament forces
Distribution and Position of Mass
External Forces

15. Biomechanics of Balance Stability
Stability is Maintained as long as the:
Internal (Stabilizing) Torques = External (Destabilizing) Torques

16. Biomechanics of Balance Factors Influencing Stability
In Practical Terms:
Sensory Factors
Motor Factors
Biomechanical Factors –
Size of the base of support
Height of the COG above the base of support
Mass

17. Biomechanics Center of Gravity
Definition – The point around which the mass of the body is equally distributed

18. Biomechanics Center of Gravity – Factors Influencing
Mass
Location of Mass – position of the body segments
Added (external) mass

19. Biomechanics of Balance Control of Balance
CNS
Motor
Sensory

20. Biomechanics of Balance Sensory Input
Purpose:
To provide the CNS with information about the direction and magnitude of De-Stabilizing Torques
To monitor the effects of Internal Stabilizing Torques
Components:
Vision
Somatosensory
Vestibular

21. Biomechanics of Balance Somatosensory
Muscle Spindles
Joint Receptors
Tendon Organs
Mechanoreceptors

22. Biomechanics of Balance Vestibular System - The Inner Ear
The Vestibular System provides information about:
Head Linear Acceleration
Head Rotation (angular accelerations)
Head Position

23. Biomechanics of Balance Sensory Input and Control
Sensory Input activates reflexes that (in order):
Activates Supporting Musculature
Activates Muscle synergies to produce correction

24. Biomechanics of Balance CNS and Control
The CNS Implements “Strategies” that are intended to be selectively applied to various levels of instability
Quiet Stance – maintained by postural alignment, associated joint stiffness and muscle tone

25. Biomechanics of Balance The Ankle Strategy
Minimal Instability – the “Ankle Strategy”
Simple Response Rotation at the ankle Inverted Pendulum

26. Biomechanics of Balance The Hip Strategy
Greater Instability – the “Hip Strategy”
More complex Increased translation of mass Adjustment at Hip

27. Biomechanics of Balance The Stepping Strategy
Maximum Instability – the “Stepping Strategy”
Most complex Multiple segments involved Slowest

28. Biomechanics of Balance Muscle Response to Instability
Muscle Response to Instability Results in a Distal to Proximal Activation Pattern
Gastroc/Soleus – 90 – 100 msec
Hamstrings – msec
Psoas – 130 – 140 msec

29. Biomechanics of Balance Can Balance Be Improved????
YES !!
Sensory Input
CNS Processing
Muscle Output
Cognitive Factors
All capable of Degradation…or…Improvement (sometimes)

30. Biomechanics of Balance Can Balance Be Improved????
Assistive Devices

31. Evaluating Balance
Force Plate